The present invention relates to a method and apparatus for manufacturing tablets of moist powder.
Conventionally, tablets are classified into molded tablets and compressed tablets. These two kinds of tablets have been manufactured by different methods. The molded tablets are manufactured by kneading an additive agent such as an excipient or a binder into medical ingredients to form a mixture, adding a solvent such as water, ethanol or the like into the mixture to produce moist powder, and forming the moist powder to have a predetermined shape by molding. There are two methods of forming the moist powder into the tablets, one of which is a thrust-filling method in which the moist powder is forcibly pressed into a die having a certain shape, and the other of which is a die-punching method in which the moist powder is processed into a plate-like material by a rolling machine and a die of a certain shape is pressed against the material for punching. The molded tablets exhibit superior solubility and collapsibility when they are taken by a patient. However, it is difficult to deal with the moist powder during manufacturing the tablets. Particularly, when the moist powder is pushed out of the die, the moist powder tends to stick to the surface of an ejector pin or rod so that there occurs dispersion in weight of tablets to be products, the surface of the tablet becomes rough, or the tablet is liable to be worn or broken because its mechanical strength is insufficient. Thus, the molded tablets are disadvantageous in respect of efficiency of production, accuracy and quality. Therefore, the molded tablets have been hardly manufactured at present.
Meanwhile, almost all the tablets now available in the market belong to the compressed tablets. An apparatus for manufacturing the compressed tablets molds dry granules at a relatively high pressure of 100 to several thousands kg/cm.sup.2. This machine is generally called a tablet machine. The tablet machine comprises an upper rod, a lower rod and a mill. By applying force from the upper and lower rods to the granules supplied in the mill, the granules are pressurized and instantaneously formed into a tablet. A rotary-type tablet machine ordinarily includes 10 to 100 sets of an upper rod, a lower rod and a mill which are attached to a turn table. By using the rotary-type tablet machine, it is possible to manufacture tablets of the same number as that of the sets of the upper and lower rods and the mill during one rotation of the turn table. There is a tablet machine having a maximum tablet manufacturing capacity of 8,000 per one minute. The compressed tablets are appropriate for mass production, and superior to the molded tablets in respect of accuracy and quality. However, since the dry granules are compressed at the high pressure, the compressed tablets are inferior to the molded tablets as for the solubility and collapsibility.
As mentioned above, although the compressed tablets are superior to the wet tablets in view of efficiency of production, the wet tablets having the excellent solubility and collapsibility are suitable for persons of advanced age and infants to take, who are low in organic and physiological function. Accordingly, by developing a method of effectively mass-producing tablets of high mechanical strength, accuracy and quality which are easy for the persons of advanced age and infants to take, without deteriorating the aforesaid characteristics of the wet tablets, a remarkable merit can be realized in the field of medicines.